BRCA2 is a human tumor suppressor gene. Like most genes, variations in the BRCA2 gene can be either causal for a given disease, or associated with somewhat higher risk, or benign. In clinical terms, a "causal" variation is usually designated as "pathogenic".

However, "causal" (or "pathogenic") does not mean that there is a 100% certainty that a person with such a variant will develop the disease. The clinical synopsis in OMIM for cancers associated with causal BRCA2 mutations is [1]:

Mutation carriers have an increased risk of developing breast and/or ovarian cancer at an earlier age

Lifetime risk of breast cancer in mutation carriers is 60 to 85%

Lifetime risk of ovarian cancer in mutation carriers is 10 to 20%

Lifetime risk of breast cancer in male mutation carriers in 6%

Increased risk of bilateral breast cancer

There are hundreds of BRCA2 variants that are considered causal/pathogenic, but almost all are very rare (far less than 1% frequency each). [There are also hundreds of other BRCA2 variants that raise one's risk just a bit; these are usually found in 1 - 3% or higher frequencies.] Perhaps the "least rare" causal BRCA2 SNP is:

rs28897756 (also known as P3039P or 9345G/A), risk allele A. Researchers suggest that a SNP in the BARD1 gene (also called BARD1 Cys557Ser) is an ancient variant that confers risk of single and multiple primary breast cancers, and this risk is amplified in carriers of the BRCA2 999del5 (codon 257, exon 9) mutation, which appears to be this SNP (rs28897756). [PMID 16768547]

The relative risk of breast cancer associated with PALB2 mutations was estimated to be 2.3 (two-fold). This is similar to the increase in risk seen with the CHEK2, ATM, and BRIP1 genes, reported by the same research group since 2002. PALB2 is the first low-risk gene protein product found that interacts with BRCA2 and all of the other low-risk genes, CHEK2, ATM, and BRIP1, are linked to BRCA1. Together, these genes are thought to account for around 2 percent of all breast cancer cases. [2]